Resistance unit



July 8, 194`.

| s. BURGETT RESISTANCE UNIT- Filed Jan. 15, 1939 0?/ ATTORNEY.

Patented July 8, 1941 BLE SISTANCE UNIT Lynn S. Burgett, Euclid, Ohio, assigner to The Clark Controller Company, Cleveland, Ohio, a

corporation of Ohio Application January 13, 1939, Serial No. 5550,778

4 Claims.

This invention relates to electrical resistance units.

As is well known in the various electrical arts, electrical resistance is interposed in electric circuits for various purposes, one such purpose, as an illustration, being to control the electric current supplied from a current source to an electric motor.

The resistance is customarily incorporated in a resistor or resistance element comprising a length of metal of preselected ohmic value, mounted en a frame or support and insulated therefrom, whereby it may be transported and installed as a unit, The unit may comprise one or more resistance elements and 'they may, in some cases, he worked at high temperatures, and the unitary construction therefore provides mechanical protection for the resistance element and a support for it even when worked at such high temperatures that the resistance element attains a red heat.

In such units, electric terminals, to which eX- ternal electric circuits may be connected, must he joined to the resistance element, and it is one of the objections to prior resistance units that this juncture deteriorates or breaks due to strain imposed upon it while connecting the electric circuit to the terminals or due to rough handlinsr or vibration while in use.

Furthermore, in such units, it has been diilicult to replace the resistance elements.

It is therefore one of the objects of this invention to provide improved means hy which the resistance element and the terminal connections to it may both be supported in an improved manner upon the frame of a resistance unit.

Other objects are:

To provide generally an improved electrical resistance unit;

To provide an electrical resistance unit ci the type comprising a frame supporting a resistance element and having improved means for supporting the element on the frame;

To provide in an electric resistance unit of the type comprising a resistance element mounted on a frame, improved means for rendering the element readily attachable to and detachable from the frame;

To provide in an electric resistance unit an improved construction of resistance element;

To provide for resistance units an improved construction of terminal connection for the re sistance element of the unit;

To provide a resistance unit having improved means for allowing contraction and expansion therein, eected by heating ci the resistance element of the unit;

Toy provide in a resistance unit of the class referred to, improved means for maintaining electric conducting connection between the resistance element and the electric terminals to which the electric circuit connections are made;

To` provide a resistance unit of the class referred to, constructed in an improved manner to facilitate assembling of the resistance element with the supporting frame.

Other objects will be apparent to those skilled in the art to which my invention appertains.

My invention is fully disclosed in the following description taken in connection with the acoompanying drawing in which:

Fig.. l is a top plan view of a resistance unit embodying my invention, with parts broken away and shown in section;

Fig. 2 and Fig. 3 are longitudinal sectional views taken respectively from the planes 2-2 and 3-3 of Fig. 1, with parts broken away, and parts behind the section planes omitted to simpliiy the drawing;

Fig. 4 and Fig. 5 are views taken respectively approximately from the planes 4 4 and 5--5 of Fig. l, with parts in section and parts broken away;

Fig. 6 is a crcss-sectional view taken from the plane 6 of Fig. l.

Referring to the drawing, the resistance unit illustrated therein comprises in general, two resistance elements I and 2 in the form of an edgewound helical strip of metal ribbon having suitable ohmic resistance per inch of length; a frame upon which the resistance elements are supported; and electrical connections by which electrical conductors may be connected to the resistance elements and by which the resistance elements may be connected to each other.

The frame comprises a pair of side bars 3 and 4 of metal disposed substantially parallel to each other on opposite sides of the frame, and connected at their opposite ends to upright supports, the side bar 3 being connected to uprights 5 and 5, and the side bar 4 being connected to uprights l and ii. The uprights preferably constitute the intermediate portions of `C-iorm metal members, the side arms of the C-iorm constituting upper and lower feet 9 and IQ respectively, having perforations l l, one in each foot, through which bolts or screws may be projected to fasten the feet and therefore the upright supports, to the wall, floor, metal frame, or the like, upon which the unit as a whole is to be mounted.

The frame comprises also frame bolts I2 and I3 which connect the side bars and uprights together into a complete frame, the bolt IZ connecting the uprights and 'I to the side bars 3 and 4 and the bolt I3 connecting the uprights and 3 to the side bars 3 and 4, and the bolts I2 and I3 also function to support the opposite ends of the resistance elements I and 2 and the electrical connection thereto. The various elements by which these functions are accomplished will now be described.

As stated above there are two resistance elements I and 2, although only one element or a greater number than two may be provided if desired, as will become apparent; and these clements are preferably alike as to structure. The resistance element I will be described in connection with Figs. l and 2, and in connection with the method of construction it.

A length of metal bar I4, preferably of steel, which, as shown in the drawing, may be approximately six times as wide as it is thick, has the intermediate portion cut away at the opposite edges thereof as at I5 and I5, thereby providing an intermediate shank I`I and at the opposite ends, heads I8 and ISI.

The head I8 is bifurcated by having a notch 2) formed therein and extending thereinto in the axial direction. The head I9 is bifurcated by having a, notch 2l cut therein entending thereinto laterally.

A pair of like insulators 22 and 23 are provided, preferably made from 'ceramic material, and, as shown in Figs. 2 and 6, having each a longitudinal groove 24 therein of such size as to straddle the edge of the shank I'I. Outwardly of the groove 24 each insulator is provided with a longitudinal series of transverse grooves 25-25, which, as shown in Fig. l, are at an inclination to the axis of the shank I'I.

The resistance element I is made by winding edgewise on a mandrel, in helical configuration, a strip of resistance metal. The helical element thus formed is telescoped over the head I9 or the head I8 of the bar I4 and threaded into the grooves 25 of the insulators 22 and 23 which have previously been placed in position on the shank II with their grooves 24 embracing the shank I7.

The insulators 22 and 23 are held on the shank I 'I by the resistance element, intermeshed therewith, and the insulators are held longitudinally in position on the shank I1 by the heads I8 and I9, the cutting away of the edges of the metal bar I 4 providing shoulders 25-26 and 2'I-2'I at opposite ends of the shank I'I upon which the ends of the insulators 22 and 23 may abut.

At, or adjacent to the opposite ends of the helically wound resistance element I, electrical connectors 2B and 29, see Figs. l and 3, are electrically and mechanically connected thereto, preferably by welding, as shown at 30.

The connectors 28 and 29 are in general of L-forin, as shown in Fig. 3. The connector 28 may be considered as comprising a leg 3I, which when in the assembled relation thereof, in Fig. l, is a vertical leg, and a corresponding horizontal leg 32; and the connector 29 may be considered as comprising a vertical leg 33 and a horizontal leg 34.

The connector 28 has formed in the intermediate portion thereof a notch 35 extending in the direction of the horizontal leg 32, and the conneetor 29 has a corresponding notch 36 extending in the direction of the leg 33.

The connectors 28 and 29 have their horizontal legs 32 and 34 extending toward each other and terminating respectively in feet 3l and 38, and the connectors 38 and 23 have their vertical legs 3I and 33 terminating in feet 38 and 4U respectively, and the said welded connection of the resistance element to the connectors is made at the feet 3l and 33.

The resistance element 2 and the connectors associated therewith, may be and preferably are, for economy and convenience cf manufacture, identical.

The two resistance units I and 2, constructed as above described and having on the opposite ends the connectors 28 and 2S are assembled with the frame elements above referred to as follows.

The bolt I2 is rigidly connected to the upright 'I and side bar 4 and insulated therefrom by telescoping over the bolt a short tube 4I of insulating material and then projecting the bolt and insulating tube through perforations in the upright and side bar, as best shown in Fig. fl. Discs 42 and 43 of insulating material are telescoped over the tube 4I, metal washers 44 and 45 are telef scoped over the bolt and against the discs 42 and 43 and a nut 4G is then threaded on the rod clamping the parts just described against the head of a thimble 4l which has previously been screwed on to the rod I2, and which has an adjusting nut 48 threaded on the outside thereof. A helical spring 4S is telescoped over the thimble.

A long insulating tube 5G is then telescoped on the bolt I2 and thereover are telescoped in the order named: a metal washer 5I, a pair of insulating washers 52, a metal tube 53, a metal washer 54, a pair of insulating washers {i5-55, a metal washer 55, a metal tube 5l, a metal washer 58, a pair of insulating washers 53-55, a metal washer S2, a metal tube SI, a metal washer 62, a pair of insulating washers an insulation ller 64, which may comprise a plurality of insulating washers, the side bar 3, the upright 5, an insulating washer 65, and a metal washer E5; and then a nut 61 is threaded on the adjacent end of the bolt I2, but not at this time drawn up tight.

A similar or identical assembly is then made upon the bolt I3 with respect to the uprights 8 and 6 and the side bars 4 and 3, as best shown in Fig. 5, except that in place of the adjusting nut 48 and spring 49, an outer thimble 68 is threaded on the thimble 4l.

The inner end of the tube 5i) may be adjacent to the end of the thirnble 4l.

The pairs of insulating washers 52, 55, 5S and 63, are then spread apart, this being permitted by the nut 6'! which is only loosely threaded on the bolt I2 at this time, and the heads I8--I8 of the resistance element are inserted between the washers 52-52 and 559-59, the notches 2-23 in the head being caused to straddle the insulating tube 5G; and similarly the connectors 28-28 are placed between the pairs of washers 55 and 53 with their notches 35 straddling the tube 5I).

In a similar manner, at the other end of the resistance element, the heads I9 are disposed between the corresponding pairs of resistance washers 'S2- 52, and 59-59, and the connectors 29-29 are disposed between the corresponding pairs of washers E5 and 63, with their notches 36 straddling the insulating tube on the bolt I3, which may be identified by the reference character 5IJA.

disposed It will be observed that, by having the notches 2| and 36 of the resistance element and connectors respectively disposed substantially at right angles to the. notches and 35 at the other end of the element, the assembling of the resistance elements and their connectors upon the bolt I3 as just des-cribed, may be performed by rocking them around the axis of the other bolt, I2, and .in this connection it may be added that it is a particular advantage of my invention, that after the assembling of the parts is completed, as will presently be described, or during the assembly thereof, any or all of the resistance elements may be readily attached and detached from the complete unit by rocking one end thereof around the bolt at the other end and then withdrawing it longitudinally, this being effected through the agency of the said relative arrangement of the notches 2li-ZI and 35-35.

With the parts all assembled as above described, the nut El on the bolt I2 and the corresponding nut 59 on the bolt I3, may be screwed inwardly on the bolts, either until the inner ends of `the tubes Sii and SQA engage the inner ends of the thimbles 4l-4'I, or until the overall dimension from the outside of the upright 5 to the outside of the upright 'I (and correspondingly for the uprights and 8) has been reached.

Thereupon the adjusting nut 48 is turned to compress the spring IIS; and the outer thimble 68 is turned to engage the adjacent Washer 5I, and by this means any desired amount of compression of the assembled parts between the nuts 51-53 and the said washers 5I-5I may be provided and the said compression will retain the side bars and uprights 3, 4, 5, 6, 'I and 8 rigidly connected in the arrangement described and illustrated, upon the bolts I2 and I3. The arrangement of the parts above described and illustrated isolates electrically the resistance elements I and 2 from the frame comprising the bolts, side bars and uprighfts; and furthermore insulates the bolts I2 and I3 themselves from the side bars and uprights.

The resistance elements may be connected in electric circuits by connecting the circuit to the feet 3S and 40 of the connectors 28 and 2B. The arrangement illustrated provides for connecting the two resistance elements I and 2 in series. To this end across connector '153, see Figs. 3 and 4, is bolted to 'the feet 353-3. of the connectors 28-28 by bolts 'II- 1I projected through perforati-ons 'I2 in the feet 39 and connector 713. Electric terminals of any suitable or known construction may be bolt-ed to the feet @5i-40. utilizingr for this purpose the perforations 'I3-J3, Fig. 5, and will be apparent. electric conductors, not shown. connected to such terminals, and therefore connected to the feet sil-Mi. will have the resistance elements l and 2 ,in series therewith. If the connector 53 'is omitted, electrical termimay be bolted to the feet 353-39, by which arrangement the resistance elements I and 2 may be placed in separate circuits or in parallel circuits, as will be understood, the circuits being connected respectively to the feet 39 and 4l), associated with each of the resistance elements.

From the foregoing construction it will be seen that the resistance element as a whole is rigidly supported at opposite ends upon the frame and that the terminal connectors H8 and 29 are also, and independently oi the resistance element, mounted upon and connected rigidly to the frame, By this means there is no possibility that the juncture, for example that at 3D, between the electrical connectors and the resistance element proper, or resistor, will be subjected to strain while electrical circuits are being connected to the connectors 23--29 in the arrangement illustrated, or to the connectors 29--28 and 28-28 when, as stated above, the resistance elements are to be connected singly in circuit.

Furthermore, although in the nal assembly the parts are dra-wn up tightly together on the bolt-s I2 and I3 as described, the resistance elements as a whole and the connectors 28 and 219 joined thereto are not under torsional or bending strain because they may rotate to free positions around the bolts I2 and I 3 before the endwise compression is applied.

If desired, in order to insure that the uprights 5, 6, l, and `ii will remain at right angles to the bars 3 and 4, the extreme ends of the bars 3 and 4 may be bent over as at 'I4--14 around the outer edges of the uprights.

As shown 'in the drawing and as described above, the means for producing the compression along the bolt I2 is eiTected by the agency of a spring 49, whereas `that on the bolt I3 is effected by direct compression of the outer thimble or nut 58. These two different arrangements provide alternative means for this purpose as either arrangement may be employed with respect to both bolts I2 and I3, if desired.

Tt may, however, be preferable to employ the spring arrangement, as illustrated for the bolt I2 for providing the compression at the ends of the resistance elements having the longitudinal notches 2s, and this arrangement is the one illustrated. The spring compression at this end of the resistance element permits longitudinal relative expansion and contraction between the frame as a whole and the resistance element bars i'I, by allowing the notches ZIJ to slide back and forth longitudinally with respect to the bolt I2.

The said adiusttnent means along the bolts I2 and I3 provide another and important advantage. The resistance unit as a wholeY is to be mounted upon a support by bolts projected through the perforations I I-I I, and corresponding perfcrations in the support, and the perforations in the support may be provided in advance of the construction of the unit. The unit must 'therefore have a corresponding perforation-toperforation spacing. Also in many cases. a number of resistance units may be mounted in a stack. one above and upon another; and in such cases the transverse spacing between a pair of holes II-II of unit must be the same as that of another in order that the holes may be axially aligned for the proiection therethrough of securing bolts. It follows that in assembling the unit, the holes H in. the feet IG of the upright 5 must be spaced from those in the feet of the upright 'I a definite predetermined distance, transversely of the unit, and that the holes II in the feet of the uprights I5 and 8 must have a like spacing.

The arrangement described, comprising the thimble All, nut d8 and spring 49 and the arrangement providing the thimble 4l and the nut $3 are in the nature of spacers of adjustable axial length. in assembling the parts along the bolts I2 and I3, they may be telescoped over the bolts as described and the nuts 46 and 61 on the bolt I2 and the nuts 45 and 69 on the bolt I3 may be put in place and adjusted on the bolts to give the said pre-determined spacing between opposite pairs of holes il-l l. Then by turning the nut 48 and the nut t8, the parts will be clamped along the respective bolts with the desired amount of compression without changing the said transverse dimension, and the transverse dimension of all of a series of such units will be exactly the same.

Furthermore, in the event that one or more resistance elements must be interchanged or replaced, it would be practically impossible to disassemble and reassemble the parts and partiearly to reassemble them to the said preselected transverse dimension of the unit, without the said adjustment feature.

My invention is not limited to the exact dctails of construction shown and described. Changes and modications may be made Within the spirit or my invention. without sacricing its advantages and within the scope oi the pcnded claims.

I claim:

l. In a resistance unit, a pair of spaced a rod extending through alig ed perforations in the rails, means securing one e;..d oi the rod tca rail said means comprising a bead on the rod outv-.f'ardly of the rail and an inwardly of the rail and clamping the tween the head and thimble, an opposite h^ad on the other end oi the rod outwardly of e other rail7 an insulation tube on the rod extending irc n the tliimble through the said other rail to opposite head, resistance carrying e :in-ents, sulators and resistance termi.A ls einbra l tube in alternate relation and means t` cxteriorly on the thinible to force the e carrying elements` insulators and ter slide on the tube toward the said other the said other` rail to slide on the tube and a.

the said opposite head.

2. In a resistance unit, a frame cori spaced side rails; a rod between the rails and supported at one end portion by one side rail, and having abutment means to prevent withdrawal therefrom toward the other rail, and the rod at its other end portion being threaded and connected to the other side rail; an insulating tube telescoped on the rod; an internally threaded thimble threaded on the rod, and rotatable thereon to exert force on an end of the tube to force the tube on the rod toward the said one rail, and to cause its other end to react on the abutment to hold the tube rigidly assembled with the rod and said one rail; a resistor comprising a bar and a resistance element thereon insulated therefrom; the bar having a notch embracing the tube; a conductinU arm connected to the resistance element and having a notch embracing the tube; insulating spacers loose on the tube, for spacing the arm and bar with respect to each other and with respect to the one side rail; a thimble nut threaded on the thimble and rotatable thereon to force the bar, arm and spacers aaien/ii to slide on the tube into a rigid tier against the one side rail; whereby upon loosening the thimble nut, the resistor and connector may be removed and replaced without loosening the assembly of the rod, and tube and said one rail.

3. In a resistance unit, a frame comprising spaced side rails; a rod between the rails and supported at one end portion by one side rail, and having abutment means to prevent withdrawal therefrom toward the other rail, and the rod at its other end portion being threaded and connected to the other side rail; an insulating tube telescoped on the rod; an internally treaded thinible threaded on the rod, and rotatable thereon to exert force on an end of the tube to force the tube on the rod toward the said one rail, and to cause its other end to react on the abutment to hold the tube rigidly assembled with the rod and said one rail; a resistor comprising a bar a resistance element thereon insulated therefrom; the bar having a notch embracing the tube; a conducting arm connected to the resistance element and having a notch embracing the tube; insulating spacers loose on the tube, for .spacing the arm and bar with respect to each other and with respect to the one side rail; a thiinble nut threaded on the thimble and a spring inwardly thereof; the thimble nut being rotatable on the thimble to cause the spring to yieldingly force the bar, arm and spacers t0 slide on the tube into a compact tier against the one side rail; whereby the bar and arm may slip relative to the rod, and whereby upon loosenthe thimble nut and spring, the resistor and connector may be removed and replaced Without looseningr the assembly of the rod, tube and said one rail.

e. In a. resistance unit, a pair of spaced side a rod extending through aligned perforations in the rails; threads on one end of the rod, a head on the rod outwardly of one rail; a rod nut on the threaded end of the rod outwardly of the other rail; an insulating tube telescoped on the rod; a thimble having internal threads ineshed with the rod threads and rotatable on the rod to eff-ect a clamping action on the tube between the thimble and the rod head; the rod nut being rotatable on the rod to clamp the other rail between it and the thimble; a resistor comprising a bar, and a resistance element thereon insulated therefrom; a conducting arm connected to the resistance element; the arm and bar having aligned perfcrations embracing the tube; a series or" insulating spacers loose on the tube and alternating with the bar and arm; a thimble nut threaded externally on the thimble and rotatable thereon to forcibly slide the insulating spacers, arm and bar along the tube to exert a clamping action thereon between the thimble nut and the rod head.

LYNN S. BURGETT. 

